Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:    BCH broadcast channel    BS base station    BSID base station identification    CID connection identifier    DCD downlink channel descriptor    DL downlink (BS to MS)    FCH frame control header    FMT format    MAC medium access control layer    MAP map messages corresponding to DL or UL    MCS modulation coding scheme    MS mobile station    MSDU medium access control layer service data unit    PHY physical layer    PSC power saving class    PSCID power saving class ID    RSV reserved    SLPID sleeping ID    SFH superframe header    UCD uplink channel descriptor    UL uplink (MS to BS)    WiMAX worldwide interoperability for microwave access
The IEEE 802.16 working group has established a new task group, 802.16m, to provide an advanced air interface to meet the IMT-Advanced requirement, and which amends IEEE 802.16-2004 (see IEEE 802.16-2004, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” Jun. 24, 2004) and 802.16e (see IEEE 802.16e-2005, “IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” Feb. 28, 2006) in order to meet the requirements of next generation mobile networks. One target of the 802.16m specification work is to provide support for enhanced power saving functionality to help reduce power consumption in devices for all services and applications (see IEEE 802.16m System Requirements, 2007-10-19).
In WiMAX, the sleep mode is intended to minimize MS power usage and decrease usage of serving BS air interface resources. For each involved MS, the BS maintains one or several contexts, each one related to certain PSC. The PSC is a group of connections that have common demand properties. There are currently three types of PSC, which differ by their parameter sets, procedures of activation/deactivation, and policies of MS availability for data transmission.
The PSC of type I is recommended for connections of best-effort, none-real-time type of services. The PSC of type I is deactivated either by a MOB_SLP-REQ/“BR and UL sleep control header”, or by MOB_SLP-RSP/DL sleep control extended subheader messages, or (if a traffic triggered wakening flag=1) after one of following events: the BS transmits (during availability window) a MSDU or fragment thereof over a connection belonging to the power saving class; the MS transmits a bandwidth request with respect to a connection belonging to the power saving class; or the MS receives a MOB_TRF-IND message indicating a presence of buffered traffic addressed to the MS. If the traffic-triggered wakening flag=0, the PSC of type I will not be deactivated, even if there are data packets transmitted to/from MSs during a listening window.
When the PSC of type I is activated, during the listening window, the MS is expected to receive all DL transmissions in the same manner as in a state of normal operations (i.e., no sleep mode activated). This means that DL-MAP/UL-MAP messages are to be received and decoded by the MS, even if MS does not need to know all the details of these messages. Note that DL-MAP/UL-MAP messages normally consume more than 10% of a frame's resources, which is a significant portion. Thus, the power of the MS is needlessly consumed for a case where the MS does not need to wake up due to an absence of a DCD/UCD change or an absence of buffered DL traffic.
MOB_SLP-REQ, MOB_SLP-RSP and MOB_TRF-IND from 6.3.2.3.44, 6.3.2.3.45 and 6.3.2.3.46 of IEEE 802.16e, respectively are described below.
A MS with a supporting sleep mode uses the MOB_SLP-REQ message to request definition and/or activation of certain PSC of types 1, 2, and 3. The MOB_SLP-REQ message is sent from the MS to the BS on the MS's basic CID. If the definition bit is set, the message contains a new PSC suggested by the MS
A MS with a supporting sleep mode will receive the MOB_SLP-RSP message. The MOB_SLP-RSP message is sent from a BS to a MS on broadcast CID or on the MS′ basic CID in response to an MOB_SLP-REQ message. The MOB_SLP-REQ message may also be sent unsolicited. If a definition bit is set, the message contains the definition of a new PSC together with an assigned PSCID. The PSCID that is unique for every MS if only unicast traffic connections are included and unique for every cell if only multicast connections are included. A mixture of multicast and unicast connections in a single class is not allowed.
Upon reception of the message, the MS assembles connections in PSCs and optionally activates them as requested in the message. If certain class activations are deferred (Activation=0), the BS may signal activation at a later time in another unsolicited MOB_SLP-RSP message.
Also of note is the MOB_TRF-IND message. This message is sent from a BS to a MS on broadcast CID or sleep mode multicast CID. The message is intended for MSs that are in sleep mode that have one or more PSCIDs of type I, and is sent during those MS's listening-intervals. Any MS without PSCIDs of type I ignore this message. The message indicates whether there has been traffic addressed to each MS that is in sleep mode. For a MS that is in sleep mode, during its listening-window the MS decodes this message to seek an indication addressed to itself.
When the MS awakens, it will check the frame number to ensure that it did not lose frame synchronization with the BS and read the SLPID-Group Indication bit-map or Traffic Indication bit-map assigned to it and decide whether to continue in sleep mode or return to normal operation.
There are two formats for the MOB_TRF-IND message, indicated by the FMT field. When FMT=0, if the MS does not find its own SLPID-Group Indication bit-map or traffic indication bit-map corresponding to its SLPID in the MOB_TRF-IND message, it will consider this as a negative indication and may continue in sleep mode. When FMT=1, if the MS does not find its own corresponding SLPID in the MOB-TRF-IND message, it will consider this as a negative indication and may continue in sleep mode.
The BS may arbitrarily include a positive indication for a MS in the MOB_TRF-IND message during the listening-window. This may occur if the MS's periodic ranging operation is scheduled to start sooner or later within the next sleep-window and there is no DL traffic to be sent to the MS.